From: "Ben
Date: Tue Oct 21 2003 - 14:16:10 GMT-3
See pages 10-14 of Cisco LAN Switching (Ciscopress) for a description
of the slotTime (51.2 msecs) and Ethernet frame sizes. I agree - it
probably relates to that.
Regards
Ben
--- Jonathan V Hays <jhays@jtan.com> wrote: > Paul,
>
> Good question. I don't know the answer but I can give you an idea.
>
> I suspect the tradeoff had more to do with CSMA/CD timing back in the
> days when ethernet was run on a shared cable. If you were deciding on
> a
> specification, you would pick a stable clock rate (for example, 10
> Mbps,
> just as a number pulled out of the air ;) which was dependent on the
> level of technology at the time (1970s I think) and a maximum cable
> length, and how long to listen on the cable before sending your frame
> (CSMA/CD). The size of the packet is obviously going to affect the
> timing for collision detection and avoidance.
>
> I think these are the factors that determined the maximum size of the
> ethernet frame in the original specs, but I'm admittedly just
> guessing.
>
> Maybe someone else knows more of the details.
>
> Jonathan
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of
> Casey, Paul (6822)
> Sent: Tuesday, October 21, 2003 6:04 AM
> To: ccielab@groupstudy.com
> Subject: Small Question....MTU size
>
>
> Hello,
>
> Can someone tell me why the MTU for IP networks is 1500 bytes.
> I konw that the standard for ethernet 1500, but I am wondering why
> this
> was
> picked..
> Why was an MTU of a1000 picked or what not an MTU of 5000.
> Also apart from ethernet why does the MTU of serial interfaces
> default
> of
> 1500 Bytes.
>
> Was this an optimal value for something..?? maybe a trade off between
> packet
> header overhead with small MTU and increasing number of errors with
> larger
> packets...??
>
> I have a problem getting a good answer for this, I asked one on the
> experts
> at work, but he said just thats the way it always was...???
>
> Any help appreicated.
> Kind regards.
> Paul.
>
>
>
>
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